Nonmechanical pumping of liquid is desirable and sometimes required for some applications where power for driving a pump is not available or is very precious, such as in a remote terrestrial location or a space laboratory. The problem is most common in space because of the lack of gravity that might otherwise be used in moving a liquid from one point to another, but the problem can also occur in terrestrial applications at remote locations.
An example of a terrestrial application is in connection with transporting oil from the arctic through a pipeline laid over tundra. The oil is first heated in a storage tank and then pumped through an elevated pipeline. Because the ground is always frozen below the surface, the pipeline is not buried and is instead elevated to a height sufficient to allow animals to pass beneath it and insulated to minimize heat loss from the oil in order to maintain its lowered viscosity. Stanchions which support the pipeline will, however, conduct heat into the tundra sufficient to cause significant thawing around the tundra. During some period of the year, the thaw may extend from one stanchion to the next, thus creating a continuous ribbon of thawed tundra that may deter animals from crossing. To prevent creation of this ribbon of thawed tundra, it is desirable to provide a heat pipe that conducts heat away from the base of each stanchion and into the air.
A heat pump operating without any mechanical motion of parts may consist of a heat exchange system in which liquid is evaporated in a space in thermal contact with the base of the stanchion. The vapor produced is then carried by a tube to a condensing space where heat is radiated into the atmosphere. Condensed liquid that accumulates in that condensing space must then be pumped back into the space in thermal contact with the base of the stanchion. The problem then is to pump the return liquid without the use of a mechanical pump and independently of gravity.
Nonmechanical pumping of liquids has been achieved in the prior art by porous materials used in wicking systems, such as that disclosed in U.S. Pat. No. 3,984,051 and by hollow capillary tubes, such as that using tapered capillary tubes disclosed in U.S. Pat. No. 3,379,855. However, these known prior-art systems have limitations, so there is a need for nonmechanical pumping systems that do not rely upon internal absorption or capillary tubes.